Please help me understand the appeal of Lego's?

I have picked up so many Lego's off of my 4 year old son's carpet that I feel like chucking them all. He received a bucket of Lego's for Christmas and he loves them. Along with Fisher Price Trio blocks which are easier to clean up in my opinion. My question is, is there a website or something you can print off instructions on how to build something? He got a bucket of Lego's for Christmas, lost the book that came in and keeps building a "Bird" with a headless man riding on it. I guess I would have to be a kid again to understand what makes these things so fun.